题目内容：
Winter-swimming has become popular in Beijing. Three years ago, few people would go swimming in the city waters. But now there is a Winter-swimming Enthusiasts' Club (冬泳爱好者协会) and it has more than 2,000 members. The oldest is 84 years of age and the youngest is only 7. The members are from all ways of life. They may be workers, peasants, soldiers, teachers, students...Though it is now the coldest part of the season and the water temperature in the city's lakes is around 0℃, many winter-swimmers still swim in the icy waters, even when it is snowing. They enjoy themselves in the lake, while the people by the side of the lake are wearing heavy clothes.
Why are so many people interested in winter-swimming? Because winter-swimming can be
good for one's health.
Bei Sha is a good example. He is 69 years old, and he once suffered from heart trouble for26 years. After ten years of winter-swimming he is now in good health. Scientists are now studying the effects of winter-swimming on health.
根据以上内容,回答题.
Among the winter-swimmers the oldest man isyears older than the youngest one. ( ) A．91
B．84
C．77
D．7
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答案解析：